title: Proton-coupled electron-transfer processes in photosystem II probed by highly resolved g-anisotropy of redox-active tyrosine YZ.
abstract: The oxidation of a redox-active tyrosine residue Y(Z) in photosystem II (PSII) is coupled with proton transfer to a hydrogen-bonded D1-His190 residue. Because of the apparent proximity of Y(Z) to the water-oxidizing complex and its redox activity, it is believed that Y(Z) plays a significant role in water oxidation in PSII. We investigated the g-anisotropy of the tyrosine radical Y(Z)(•) to provide insight into the mechanism of Y(Z)(•) proton-coupled electron transfer in Mn-depleted PSII. The anisotropy was highly resolved by electron paramagnetic resonance spectroscopy at the W-band (94.9 GHz) using PSII single crystals. The g(X)-component along the phenolic C-O bond of Y(Z)(•) was calculated by density functional theory (DFT). It was concluded from the highly resolved g-anisotropy that Y(Z) loses a phenol proton to D1-His190 upon tyrosine oxidation, and D1-His190 redonates the same proton back to Y(Z)(•) upon reduction.
authors.affiliation: Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Katahira-2-1-1, Aobaku, Sendai 980-8577, Japan. hmatsu@tagen.tohoku.ac.jp
authors.forename: Hideto
authors.initials: H
authors.lastname: Matsuoka
authors.forename: Jian-Ren
authors.initials: JR
authors.lastname: Shen
authors.forename: Asako
authors.initials: A
authors.lastname: Kawamori
authors.forename: Kei
authors.initials: K
authors.lastname: Nishiyama
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Ohba
authors.forename: Seigo
authors.initials: S
authors.lastname: Yamauchi
mesh_terms: D016880:Anisotropy; D004579:Electron Transport; D008968:Molecular Conformation; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000737:chemistry / Q000378:metabolism*; D011522:Protons; D011789:Quantum Theory; D014443:Tyrosine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D045332:Photosystem II Protein Complex; D011522:Protons; C114979:tyrosyl radical YZ; D014443:Tyrosine